Mr Paterson's departure follows a wide-ranging reshuffle announced on Prime Minister David Cameron’s Twitter feed.
His 38-year-old replacement, who entered parliament in 2010, will leave a ministerial role at the Department for Education.
Ms Truss founded the Free Enterprise Group of Conservative MPs which campaigns for economic reform and a positive attitude to profit making enterprise.
She is a co-author of ‘After the Coalition’, which seeks to challenge the consensus that Britain’s economic decline is inevitable by arguing for the return of a more entrepreneurial and meritocratic culture.
From her website - what has the new SoS said on farming issues?
'Farming is a vital industry in the constituency.'
'Concerns are being raised regarding changes in the implementation of the European Union’s Common Agricultural Policy (CAP). As a result of this Elizabeth led a delegation of local farmers to meet Farming Minister George Eustice MP.'
'Elizabeth has a number of concerns about the use of agricultural land for solar or biomass plants and the subsidies for these operations. She does not want to see the UK’s food security jeopardised.'
'Food and farming is the largest manufacturing industry in the UK and she is keen to see that the importance of this sector is recognised.'
'She has long argued that the £1:£8 cost benefit ratio formula provided by the Environment Agency for the funding of flood prevention schemes do not value farmland high enough.'
The new Secretary of State worked in the energy and telecommunications industry for ten years as a commercial manager and economics director and is a qualified management accountant.
She said: “I look forward to tackling the important issues facing our rural communities including championing British food, protecting people from flooding and improving the environment.”
Liz Truss is the new Secretary of State for Environment, Food and Rural Affairs.
— David Cameron (@David_Cameron) July 15, 2014
NFU President Meurig Raymond said: “Farmers grow and produce the raw ingredients for one of the country’s most successful sectors; food and drink, worth some £92 billion to the UK economy. I look forward to meeting with Liz Truss at the earliest opportunity and working together on some of the key issues facing our sector.
“I would like to take this opportunity to thank Owen Paterson for his hard work and dedication to farming and agriculture over the past two years.
“He showed an understanding of farmers and the farming industry and knew how important food production and food security is.”
NFU East Anglia regional director Pamela Forbes said: “We would like to congratulate Liz Truss on her new role and we look forward to working with her.
“She recognises that agriculture is a vital industry and she has taken a keen interest in food and farming issues in her constituency, particularly around food and water security.
“After the last drought she arranged for farmers to meet the minister to discuss concerns about water supplies for irrigated crops in Norfolk and Suffolk and she has called for greater protection for farmland from flooding.
“She also knows our views regarding reform of the Common Agricultural Policy, having led a delegation to meet farming minister George Eustice in December.”